Ennis Robert, Cao Dingcai, Lee Barry B, Zaidi Qasim
Graduate Center for Vision Research, State University of New York, New York, New York.
Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois.
J Neurosci. 2014 Jun 11;34(24):8119-29. doi: 10.1523/JNEUROSCI.1048-14.2014.
The effects of context on visual sensitivity are well established (e.g., sensitivity to luminance flicker is substantially higher on mean-gray surrounds than on white or black surrounds). The neural mechanisms generating context effects, however, remain unresolved. In the absence of direct tests, some theories invoke enhancement of edges by lateral inhibition, whereas others rely on transients caused by miniature eye movements that maintain fixation. We first replicated the luminance results on human observers and found unexpectedly that sensitivity to red-green flicker is also affected by surround color, being substantially higher on mean-gray surrounds than on red or green surrounds. To identify the neural bases of both context effects, we used in vivo electrophysiological recordings of primate magnocellular and parvocellular ganglion cell responses to luminance and red-green modulations, respectively. To test neuronal sensitivity to stationary edge contrast, neuronal responses were measured at various distances from the modulation edge against various surrounds. We found no evidence of enhanced responses to stationary edges on any surrounds, ruling out lateral inhibition-type explanations. To simulate the effects of eye movements, target patches were abruptly displaced while measuring responses. Abruptly displaced edges evoked vigorous transient responses that were selective for modulation-phase on mean-gray surrounds, but were phase-invariant on other surrounds. Eye movements could thus enhance detection of flicker on mean-gray surrounds, and neurometric analyses supported a primary role for eye movements in enhancing sensitivity. In addition, the transformation of spatial edges to transient neuronal responses by eye movements provides the signals for detecting luminance and color edges in natural scenes.
背景对视觉敏感度的影响已得到充分证实（例如，对亮度闪烁的敏感度在平均灰色背景下比在白色或黑色背景下要高得多）。然而，产生背景效应的神经机制仍未得到解决。在缺乏直接测试的情况下，一些理论认为是通过侧向抑制增强边缘，而另一些理论则依赖于维持注视的微小眼球运动所引起的瞬变。我们首先在人类观察者身上重现了亮度方面的结果，并且意外地发现对红 - 绿闪烁的敏感度也受到背景颜色的影响，在平均灰色背景下比在红色或绿色背景下要高得多。为了确定这两种背景效应的神经基础，我们分别对灵长类动物大细胞和小细胞神经节细胞对亮度和红 - 绿调制的反应进行了活体电生理记录。为了测试神经元对静态边缘对比度的敏感度，在与调制边缘不同距离处针对不同背景测量神经元反应。我们没有发现任何背景上对静态边缘反应增强的证据，排除了侧向抑制类型的解释。为了模拟眼球运动的影响，在测量反应时突然移动目标斑块。突然移动的边缘在平均灰色背景上引发了强烈的瞬变反应，这些反应对调制相位具有选择性，但在其他背景上则与相位无关。因此，眼球运动可以增强在平均灰色背景上对闪烁的检测，并且神经测量分析支持眼球运动在增强敏感度方面的主要作用。此外，眼球运动将空间边缘转化为瞬态神经元反应，为检测自然场景中的亮度和颜色边缘提供了信号。
